1. Field of the Invention
The present invention relates to the purification of silane, and, more especially, to the purification of silane gas by the sorption of impurities therefrom, such as, for example, the arsine and phosphine values.
2. Description of the Prior Art
Silane is a gas which, by thermal cracking for example, yields silicon, an especially valuable compound used for the production of a variety of electronic components. The silicon used for the production of such electronic components must be of a very high purity
To attain such a purity, it is necessary to prepare the silicon from a very pure silane and in particular to reduce to a minimum the impurities of arsine or phosphine type. It is thus imperative to purify the silane prior to the cracking stage in order to reduce the impurity content and, in particular, to reduce the impurity content thereof to less than 10 ppb (parts per billion).
This purification is typically carried out by methods such as distillation or adsorption onto molecular sieves.
It has thus been proposed to this art to adsorb the phosphine and/or arsines onto molecular sieves comprising zeolites of the A or X type. However, these molecular sieves have the disadvantage of adsorbing a portion of the silane, which militates against high yields of purification. Furthermore, if a high purity silane is to be realized, it is necessary to subject it to several successive passes through the molecular sieve, with concomitant loss of silane by adsorption during each pass.
To eliminate these disadvantages, it was proposed in the Japanese application published under No. 84/30,711 to use an A type zeolite exchanged with the Ag.sup.+ cation, thus permitting the selective adsorption of arsine and phosphine values relative to the silane.